This invention relates generally to control systems of machine tools, and more particularly to a type thereof capable of controlling machine tool or tools in a fully automatic manner.
In conventional machine-tool control systems of the above described type, the machine tools and their peripheral apparatus, for instance, conveyors for the workpieces, cutting-scrap handling apparatus, and tool magazine transporting apparatus, have been so constructed that they are operable independently.
Accordingly, when it is desired to operate these machine tools and their peripheral apparatus as one system, while maintaining a predetermined relationship between each other, there must be provided a supervisory apparatus (such as a computer) which delivers instructions, for instance, for starting, stopping, and restarting the machine tools and the peripheral apparatus, or otherwise each machine tool must be provided with a loop circuit capable of generating a restarting signal.
In the former case where a supervisory apparatus is provided, however, when the operation of the system includes the conveyance of the workpiece, and the retraction of required parts at the time of abnormal cutting operation and the replacement of the cutting tool or the like, both require wide movements of the machine tool with respect to various axes (hereinafter referred to axis-movements of the machine tool), the control system becomes highly complicated, thus increasing cost and reducing the adaptability of the control system.
In the case where loop circuits are provided in the machine tools, there is a possibility of accidental operation of such loop circuits thereby causing dangerous unattended operation of restarting and stopping the machine tools.
Also known is a control system wherein the supervisory computer includes a part common for the operations (such as distribution of data and on-off control of the cycle start) of the ordinary numerical control (NC) devices of the NC type machine tools, and at this time each NC device of the machine tool carries out remaining part of the NC operation, such as interpolation and else. However, such an arrangement is also found to have problems in the cost and the adaptability.
As is widely known, present-day machine tools constituting the components of the control system have their own NC devices, and the conveyor apparatus and the like also have their own controllers, all of the NC devices and the controllers being operable independently.
In order that an NC device is capable of suitably, controlling the corresponding machine tool, there must be provided an interface between the NC device and the machine tool, through which are executed most of the sequential operations other than those accompanying the axis-movements of the machine tool. Furthermore, the controllers themselves of the conveyors and the like are also provided with interfaces regardless of whether instruction input means are provided for each controller or not. Thus, where a system comprising the above described components is to be operated fully automatically, although the controls accompanying no such axis-movements of the machine tools are carried out through interfaces, the controls accompanying the axis-movements of the machine tools are carried out separately (this point constitutes no problem if the numerical control devices are of the CNC (computerized NC) type including sequential controls of the machine tools).
In the operation of the above described control systems, there are many problems to be solved including:
(1) On-off control of the power source at designated time instants.
(2) Operation control of each machine control unit (interface+NC device).
In response to those signals indicative of, for instance, the completion of machining, occurrence of any abnormal cutting, and alarming condition or the like arising in the course of the operation of each independent machine tool, it is required that various signals such as for restarting, retract cycles, alarming and the like be sent out to the machine control unit MCU. Otherwise, if it is required, a sequence control of each MCU must be carried out. (When the tact-time is different, the status of each machine tool should also be displayed.)
(3) Calling out of a program as a part-program at one time. Since the required part-program is made apparent from the pallet code or from the sequence of the entire system or else, this part-program is read out from a memory area where the part-program is stored, and then executed.
As for the problem (1) described above, known is a control operation wherein the power source is turned off at a predetermined time in night (timer-setting systems). However, no warming-up operation of machine tools have yet been practiced.
As for the problem (2), there has been proposed a control system in the form of a loop circuit wherein Cycle-Start is generated after the completion of a machining step, thereby rewinding and restarting the tape. However, this method is dangerous, and it is almost impossible to carry out necessary countermeasures upon sensing the alarm of an abnormal cutting or else, and to continue the fully automatic control of the machine tools thereafter.
As for the problem (3), as a matter of course, a block-by-block designation of the content of a part program to be executed has not yet been attempted.